1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing compression-coded moving image data to and from a medium (e.g., tape recording medium) such as a digital VTR (video tape recorder), and more specifically to a moving image recording and reproducing apparatus suitable for use in a special reproduction such as high speed image search, for instance.
2. Description of the Prior Art
In the VTR, some special reproductions such as high speed search are often required. In particular, the high speed image search (referred to as high speed search, hereinafter) is essential, by which images can be reproduced at a high speed 5 to 50 times higher than the ordinary (standard) reproduction speed. In the case of the high speed search, since image data recorded by helical scanning are read obliquely along the recording tracks, the image is obtained with partial ommissions. As a result, in the case of an analog VTR, one picture is displayed being divided into several portions.
In the case of the digital VTR, on the other hand, usually the high efficiency coding technique is adopted; that is, image data is compressed in accordance with a variable length coding technique. In this case, since the positions at which image data is recorded on a tape will not synchronize with the positions at which the image data is displayed on the picture, the image data displayed during high speed search fluctuates in position on the displayed picture, so that the obtained picture is extremely hard to see.
To overcome this problem, there has been proposed such a method of recording image data for only the high speed search, wherein the data is recorded separately at predetermined positions on a tape. In this method, high speed search data is recorded at predetermined several positions along the track direction, and the same data is repeatedly recorded over ten tracks, for instance. In this method, if the high speed search is conducted up to ten time speed (a speed ten times higher than the standard tape travel speed), since at least one of the ten tracks can be read without fail, all the data for high speed search can be obtained securely, with the result that it is possible to obtain a high speed search image of perfect frames or fields. Further, in the following description, the high speed search of only frames will be explained in detail.
In this method, however, since the high speed search data recorded on predetermined positions on the tracks becomes large, data for one frame cannot be recorded on one track, so that data for one frame is divided into several units of data. For instance, when data for one frame is divided into ten, the divided data is recorded over the ten tracks. As a result, when recorded repeatedly over the ten tracks as described above, the high speed search data for one frame is recorded over the 100 tracks.
In the conventional method of recording the high speed search data, however, since the same search data must be recorded repeatedly many times (the same as the magnification of the high speed search speed); that is, since the number of repetitions increases with increasing search speed, a great number of tracks are required to record search data for only one frame or one field. As a result, the number of frames for the recorded search image decreases, so that the frames of the reproduced search image tend to become insufficient.
In addition, in the conventional method of recording the high speed search data, since the ranges at which the ordinary reproduction moving image data is recorded and the regions at which the special reproduction (search) data are recorded is both fixed on the tape, the respective recording transfer rates thereof are decided separately. Accordingly, when the transfer rate of the moving image data to be recorded is low, the moving image data is recorded by inserting some blank (stuff) data therebetween. On the other hand, the image data for special reproduction is recorded at a constant transfer rate, irrespective of the transfer rate of the moving image data.
Further, since the image data for the special reproduction (e.g., high speed search) repeatedly must be recorded many times (e.g., the same as the magnification of the high speed search), it is difficult to secure a sufficient transfer rate, with the result that there exists such a problem in that the resolution is lowered and the number of frames of the special reproduction image data decreases.